The present invention relates to improvements in wrench socket designs which redistribute and reduce the internal stresses exerted on the socket during driving and which improve the driving performance of the socket by providing a driving surface at an angle which best matches the fastener face to be driven.
When designing socket wrench openings, to avoid breakage of the wrench and/or deformation of the fastener, it is desirable to minimize the stress exerted on the socket. It is likewise desirable to distribute, as uniformly as possible, the stress exerted on the socket. Stress analysis indicates that three important points of high stress exist when a socket wrench engages the flank or face of a hexagonal or double hexagonal fastener. The first area of stress is where the wrench driving surface meets the fastener face. It is desirable that this surface be as large as possible to more uniformly distribute the stress throughout the socket. It is also important that the drive surface be, as nearly as possible, parallel to the fastener face to minimize peak stress. This is achieved by orienting the drive surface at an angle which takes into account the position of the wrench when it engages the fastener. In this respect, a small clearance exists between the internal socket surface and the fastener to be driven. As this clearance is taken up in turning the wrench to engage the fastener, the wrench is angularly displaced relative to the fastener. Thus, there is a need to choose an angle for the wrench driving surfaces of the socket which best matches that of the fastener when the wrench is in the angularly displaced position.
The second important area of stress concentration is at the outer edge where the driving surface of the socket wrench ceases to contact the fastener, i.e. at the corner of the fastener. Because there is an abrupt contact pressure area at the corner of the fastener which results in an abrupt stress peak, it is desirable that the driving surface not contact the fastener at the corner thereof.
The third area of stress concentration is the portion of the wrench socket adapted to receive the corner of the fastener. In conventional wrench design, this area is a sharp arcuate angle which acts to concentrate the stress exerted on the socket.
The present invention provides a socket wrench opening which maximizes the drive face, avoids contact with the corner of the fastener, and eliminates a sharp angle, i.e. corner, and further provides a wrench socket opening shape which lends itself to efficient, reproducible, and economical manufacture.